im wondering how can you calculate on how much water say 96% H2SO4 or even 98% H2SO4 would take up from another acid (HNO3 62%?)
i mean, isnt there an azeotrope between water and H2SO4 starting at 70%? would that mean per 100 mL 98% H2SO4 you would be able to remove 28% H2O from
something else thats 100 mL aswell or how does it work??
i really cant figure it out, and not really sure what to look for to explain this.. blogfast25 - 10-3-2013 at 09:56
I doubt (but this just a hunch) that H2SO4 remain hygroscopic much below, say 90 %...
Also, without intimate contact, mass (water) transfer between the nitric and sulphuric acid must be painstakingly slow.Fantasma4500 - 10-3-2013 at 10:55
I doubt (but this just a hunch) that H2SO4 remain hygroscopic much below, say 90 %...
Also, without intimate contact, mass (water) transfer between the nitric and sulphuric acid must be painstakingly slow.
i think you must have understood it as in trying to dehydrate HNO3 without contact.. i dont think thats possible beyond a certain % of HNO3 actually..
i was thinking as making nitration acid, i know it might be more ideal to just make some nitrate and mix the nitrate with the sulfuric acid, but.. how
could i possibly calculate how much sulfuric acid i would need to dehydrate HNO3 (perhaps also for destillation of ~99% HNO3?)AndersHoveland - 10-3-2013 at 11:27
Both H2SO4 and HNO3 are acids. You would need to calculate the relative ratios of the hydrogen molecular weight to the rest of the molecule. In the
case of H3SO4, you would only use 1 of the hydrogens, since the other does not ionize off so easily. After you do this, you can get some idea of the
relative concentration of hydrogen ions in each concentration of acid.
When we talk of acid concentration, what is really of importance is hydrogen concentration (at least the hydrogens that can ionize off). What makes
concentrated acids so reactive is that the hydrogen ion is not complexed to a water molecule (which forms the hydronium ion,
H3O+ )
If you mix 1 part of 50% by weight nitric acid with 1 part 100% sulfuric acid, the mixture will contain the equivalent of
Molar mass of H2SO4 - 98 g/mol
Molar mass of HNO3 - 63 g/mol
Molar mass of H atom - 1 g/mol
( 1 / 98 )(1.00) = 0.01 , so the sulfuric acid contains 1% (reactive) hydrogen
( 1 / 63 )(0.50) = 0.008 , so the nitric acid contains 0.8% hydrogen
Since we a mixing them in a 1 part to 1 part ratio...
(0.01 + 0.008)/2 = 0.009
So the mixed acids will contain 0.9% reactive hydrogen.
Then you have to calculate how much water is in the mixture.
It is fairly easy in this example, there resulting solution will contain 25% water by weight.
Then take the ratio of hydrogen to water, and that will give you a good idea of the relative acidic strength of the solution.
we can convert the weights back into molar ammounts,
Thus the ratio is 0.648 hydrogen ions to each water molecule.
Actually, it is a little more complicated than this, since the bisulfate and nitrate ions can themselves also be protonated. Since the protonation of
the nitrate ion is part of the mechanism of nitration, that need not be considered because it is essentially synonymous with the acid strength for
your purposes here.
As you can see, it takes some calculations, but it is possible to get some idea of the equivalent acid strength of a mixture of two acids.
Obviously the nitration will procede much faster and more readily if you can get the ratio of the reactive hydrogen to be greater than 1 for every
water molecule.
[Edited on 10-3-2013 by AndersHoveland]Fantasma4500 - 11-3-2013 at 00:24
so the moles of water in the HNO3 (62% or 38g / 100g) has a link with the active hydrogen in the H2SO4?
i always thought that the H2SO4 was just used for dragging the water out of the HNO3 to get ~99% fuming, and lower the H2SO4 concentration.. blogfast25 - 11-3-2013 at 04:21
Actually, it is a little more complicated than this, since the bisulfate and nitrate ions can themselves also be protonated.
No, 'actually', it's A LOT more complicated than that. Acid base theory really applies only to fairly dilute solutions. Here you're mixing a
concentrated acid with a high concentration one.
Your calculations are worth diddly. 'Pretty nonsense', in other words.
